Beamline BW1: X-Ray Undulator

X-Ray Undulator Beamline

The BW1 X-ray undulator is the first insertion device of the new bypass section of DORIS III. The optical components of this beamline are designed to use the 1st and 3rd harmonic of the undulator in the photon energy ranges 3 - 6 keV and 9 -15 keV.

There are four user-modes, i) focused white beam using both mirrors with a cut-off energy of approximately 11 keV, ii) focused monochromatic beam using both mirrors (cut-off energy of approximately 12 keV) and the double crystal monochromator, iii) unfocused monochromatic beam using the monochromator without mirrors and iv) monochromatic beam focused by a sagittally focusing second monochromator crystal.

The monochromator is a (+/-) double crystal fixed exit monochromator under vacuum. The first crystal is directly water cooled to reduce the thermal distortion induced by the high heat load of the white beam. Each crystal is mounted on a piezo-driven micro -goniometer in order to stabilize the intensity of the monochromatic beam. A feedback system with absolute position readout corrects the hysteresis of the piezo crystals.

The first Si-mirror consists of three different reflecting parts (i) flat, Au-coated, ii) cylindrical sagittally focusing, Au-coated, (iii) flat, uncoated. The second mirror is a flat, gold coated mirror with bender to focus the beam at various sample distances.

Applications

BW1 diffractometer
XAFS spectroscopy
UHV-XSW chamber

Literature on Instrumentation

R. Treusch: "Charakterisierung und Test einer Synchrotronstrahlungsoptik für DORIS III", Diploma Thesis, Hamburg, Germany 1992 (in German)
R. Frahm, J. Weigelt, G. Meyer and G. Materlik: X-ray undulator beamline BW1 at DORIS III, Rev. Sci. Instruments 66 (1995) 1677

Instrument Specification


Source (4.5 GeV)	127-pole undulator ( Λ = 3.14 cm) with a variable magnetic gap (B_max = 0.46 T with 15.6 mm gap, K_max = 1.34, 3rd harmonic at 9.1 keV)
Mirrors	1st: flat Si / cylindrical, Au coated/ flat, Au coated; 2nd: flat, Au coated with mirror bender
Monochromator	fixed exit double crystal monochromator (+/-), vertical beam offset 150 mm, directly water cooled first Si(111) crystal, feedback system with piezo driven micro-goniometer on both crystals
Windows	in direct white beam in front of monochr.: 20 µm C-foil behind monochromator: 20 µm C-foil, front end for experiments with white beam: 1 mm Be-window, front end for experiments with a monochromatic beam: 0,4 mm Be-window He-path, 20 µm Al-foil (not necessary in case of UHV experiments which, can be directly attached to the beamline)
Operational Modes	focused white beam from 5 keV to 11 keV (1st mirror 6.5 mrad, 2nd mirror 6.5 mrad) focused monochromatic beam from 3 keV to 12 keV, (cylindrical mirror 6 mrad, double crystal monochromator, bent mirror 6 mrad) unfocused monochromatic beam (double crystal monochromator) focused monochromatic beam without mirrors (double crystal monochromator with sagittally focusing 2nd crystal)
Source to sample distance	34 m - 40

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